Variable transfer rate control coding apparatus, reproducing apparatus and recording medium

ABSTRACT

A variable transfer rate control coding apparatus which can distribute codes of an amount most suitable to the contents of a moving picture to be recorded and to a recording medium, on which information is recorded by this transfer rate coding apparatus, by obtaining an amount of codes to be temporarily generated in each unit period of time by a temporary or tentative coding, and then storing a temporary transfer rate (namely, a value of the temporary amount of codes to be generated in each unit period of time), and setting a target transfer rate (namely, a target value of an amount) of codes to be sent in each unit period of time from a total of the temporary transfer rates and the recordable capacity of the recording medium and next performing an actual or real coding according to the target transfer rates.

This application is a continuation of application Ser. No. 08/142,280filed Oct. 28, 1993, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of The Invention

This invention generally relates to a highly-efficient encodingtechnique to be employed for efficiently performing a coding (orencoding) in digital-signal recording, transmission and displayapparatuses to generate a smaller amount of codes (hereunder sometimesreferred to simply as code amount). More particularly, this inventionrelates to a coding apparatus adapted to perform a coding of a movingpicture signal by controlling a transfer rate and also relates to arecording medium on which a code generated by the coding apparatus isrecorded. Further, this invention relates to a reproducing apparatus forreading moving picture information from the recording medium. Moreparticularly, this invention relates to a variable transfer raterecording information reproducing apparatus for reproducing movingpicture information recorded on a recording medium, which informationrepresents a code generated by changing an amount of informationcorresponding to a predetermined period of time, and also relates to therecording medium on which the moving picture information is recorded.

2. Description of The Related Art

When a variable length code is used in performing a highly efficientcoding of an image signal, a part of an image represented by the imagesignal, which part contains a small amount of image information, iscoded or converted into a small amount of codes. Therefore, it isreasonable for increasing the efficiency of coding to employ a variablelength coding. Especially, in case of an inter-image predictive codingof each frame or field of a moving picture, an amount of codescorresponding to a part having no motion is very little. Thus, theefficiency of transmission or recording of information or codes can beincreased if the transmission or recording is effected by making thevisual picture quality of a moving picture nearly constant and changinga transfer rate according to an aspect of the moving picture.

Such a way of transmitting information is called an asynchronoustransmission mode (ATM) which is extensively studied as a packettransmission in the field of communication. In this case, basically,codes are generated at a predetermined transfer rate. Further, packets(or cells) are discarded on a transmission network if necessary. Thus,an amount of information or codes is controlled.

Meanwhile, in case of recording media termed package media (for example,a video tape recorder (VTR), a video disk or the like as presentlyused), information is recorded thereon at predetermined tape speed or apredetermined rotational speed. As the result, an amount of informationrecorded on the recording medium in a unit period of time (or a unittime slot) becomes constant. Therefore, the capacity of the recordingmedium can be indicated in terms of the length of available recordingtime. For instance, in case that a moving picture of 100 minutes isrecorded on a recording medium whose maximum recording time is 120minutes, the remaining capacity of the recording medium corresponding tothe recording time of 20 minutes is space for recording another picture.

To make the most of the capacity of a recording medium, a transfer rateshould be changed according to the contents of a picture to be recordedand thus the total amount of codes recorded thereon should be suited tothe capacity thereof. However, in case of a conventional codingapparatus, the transfer rate is fixed to a constant value as will bedescribed hereinbelow by referring to FIG. 1.

FIG. 1 is a schematic block diagram for illustrating the configurationof an example of the conventional coding apparatus. Incidentally, thecoding apparatus of FIG. 1 is in conformity with CCITT (InternationalTelegraph and Telephone Consultative Committee) specified standardsystem.

As shown in this figure, image signals are inputted to a predictivesubtracter 2 and an activity detector 4 through an image input terminal31. Incidentally, what is called activity indicates a degree of changein data, which is represented by an image signal, between adjacentblocks. In the predictive subtracter 2, an inter-frame prediction signal(hereunder sometimes referred to simply as a prediction signal) inputtedfrom an inter-image predicting device 13 is subtracted from the imagesignal. Then, a prediction residual signal representing a result of thesubtraction is outputted from the predictive subtractor 2 to a discretecosine transform (DCT) device 3.

Next, in the DCT device 3, a DCT is performed on the prediction residualsignal. Then, a signal representing a result of the DCT is outputtedfrom the DCT device 3 to a quantizer 6 whereupon a quantization iseffected according to a quantization step width (namely, a quantizationstep size) designated by information inputted from a quantizationcontroller 5 thereon.

The quantized signal is next inputted to a variable length coder 7 and alocal decoder 15. Further, in the device 7, information represented bythe inputted signal is converted into a compressed code. Subsequently, asignal representing the compressed code is inputted to a buffer 32. Notethat data (namely, the compressed code) inputted to the buffer 32 isconverted by the device 7 into a variable length code. Thus, an amountof generated codes changes or fluctuates constantly. However, suchchange in amount of the generated codes is absorbed by the buffer 32. Asthe result, the generated code is outputted to a decoding apparatus(shown in FIG. 3) from a code output terminal 11 at a constant transferrate.

On the other hand, in the local decoder 15, an inverse quantization andan inverse DCT are performed on the quantized signal inputted thereto.Thereby, the code is decoded and as a consequence, a reproducedprediction residual signal is produced. Then, the reproduced predictionresidual signal is inputted to an adder 14 whereupon the inter-frameprediction signal inputted from the inter-image predicting device 13 isadded to the reproduced prediction residual signal inputted from thelocal decoder 15. Subsequently, a reproduced image signal representing aresult of this addition is supplied to an inter-image predicting device13 whereupon the reproduced image signal is delayed by one frame and amotion compensation is effected to generate an inter-frame predictionsignal. The generated inter-frame signal is supplied from theinter-image predicting device 13 to the prediction subtracter 2 and theadder 14.

Further, the quantization is controlled according to what is called anoccupancy of the buffer and to the activity of an original image.

Thus, information representing the occupancy of the buffer 32 and theactivity detected by the activity detecting device 4 is inputted to thequantization controller 5 whereupon a quantization step width is setaccording to the inputted information. Further, a signal indicating thequantization step width is inputted to the quantizer 6. Incidentally,the quantization step width is set in such a manner to be wide (namely,quantization is coarse) when many codes are stored in the buffer 32 andto be narrow (namely, quantization is fine) when the buffer 32 is almostempty. Such a characteristic of the quantization step width is shown inFIG. 2.

FIG. 2 is a diagram for illustrating the manner of the quantizationcontrol, which shows an example of the relation between the occupancy ofthe buffer and the quantization step width.

In case of controlling the quantization according to the activity, thequantization step width is wide (namely, the quantization is coarse)when the activity is large. Further, the quantization step width isnarrow (namely, the quantization is fine).

This is due to the fact that in case of a block having large activity,change in image signal is large and that an error is not noticeable andthat in contrast, in case of a block having small activity, even a smallerror is conspicuous.

Practically, the value of the quantization step width set according tothe occupancy of the buffer is multiplied by a multiplier which rangesfrom (½) to 2 and is set according to the activity regarding each block.

At that time, if the average value of the activity is 1, the averagevalue of the quantization step width does not change.

In case of this conventional coding apparatus, for instance, a varianceof tone levels (or density levels) of pixels of a block is employed asan activity. Incidentally, when using DCT or the like, a quantizationerror is conspicuous in a block of an edge portion. Therefore, it ispreferable that an edge portion is detected before the activity isdetermined, and subsequently, the activity of a block of the detectededge portion is regulated in such a way not to become large.

By using the activity of an input image as described above, subjectivevisual picture quality can be made to be uniform.

Next, a conventional decoding apparatus will be described hereinbelow byreferring to FIG. 3.

FIG. 3 is a schematic block diagram for illustrating the configurationof an example of the conventional decoding apparatus.

As shown in this figure, codes inputted from a code input terminal 20 toa buffer 41 at a constant transfer rate are outputted to a variablelength decoder 22 in synchronization with a processing to be effectedtherein.

In he variable length decoder 22, the variable length code is convertedinto a fixed length code. Then, in the dequantizer 23, the fixed lengthcode is converted into a quantization representative value (hereundersometimes referred to simply as a quantization representative). Thequantization representative is inputted to an inverse DCT device 24whereupon an inverse DCT is performed on the quantization representativeto produce a reproduction predictive residual signal. Then, thereproduction predictive residual signal is applied to the adder 14.

Next, in the adder 14, a prediction signal inputted from the inter-imagepredictor 13 is added to the reproduction predictive residual signal togenerate a signal (hereunder referred to as a reproduced image signal)representing a reproduced image. This reproduced image signal isoutputted from an image output terminal 25. Further, the reproducedimage signal is also inputted to the inter-image predictor 13.

However, as described above, in case of the conventional codingapparatus, the transfer rate is controlled in such a manner to beconstant. Thus, the conventional coding apparatus has a drawback in thatalthough an amount of codes corresponding to a portion of an image issufficient and a corresponding quantization step width is too narrow, anamount of codes corresponding to another portion of the image isinsufficient and a corresponding quantization step width is large(namely, quantization is coarse) and thus the picture quality isdegraded.

Further, in case of the conventional coding apparatus, a coding isperformed at a constant transfer rate irrespective of the length (orduration) of a moving picture. Thus, the conventional coding apparatushas another drawback in that if the length of a moving picture isshorter than the maximum recordable time of a recording medium to beused to record the moving picture, a part of the recordable area of therecording medium remains unused.

Meanwhile, in case of an apparatus for reproducing information from arecording medium as above described, it is usual that informationrepresenting an image or an audio is continuously read and reproducedfrom the medium and thus there is no necessity of special control ofreproduction of the information.

In case of a constant-line-velocity (CLV) disk medium is which a linevelocity is constant, a rotational frequency should be changed accordingto the position on a disk. However the rotational frequency dose doesnot depend on the contents of information (for example, an amount ofcodes corresponding to information to be recorded for a predeterminedperiod of time) but depend depends on the position on the disk.

It is preferable for making the most of the capacity of a recordingmedium that the transfer rate for transferring image information to berecorded is changed according to the contents of a picture to berecorded (for instance, an amount of codes corresponding to apredetermined period of time) in such a manner to vary with portions ofan image represented by the image information and that the imageinformation is recorded as what is called variable transfer rateinformation and is reproduced from the recorded variable transfer rateinformation.

However, in case of the conventional coding apparatus, it is notpossible that the relative speed between a recording medium and areproducing head is changed frequency and quickly according to thetransfer rate for transferring the variable transfer rate information.Thus, in case of the conventional coding apparatus, moving pictureinformation is first recorded at a fixed transfer rate. Thereafter, therecorded moving picture information is continuously read as fixedtransfer rate information. Therefore, the prior art has a drawback inthat variable transfer rate information can not be reproduced from arecording medium on which the variable transfer rate information isrecorded by changing the transfer rate each predetermined period oftime.

The present invention is accomplished to eliminate the above describeddrawbacks of the prior art.

It is, therefore, an object of the present invention to provide avariable transfer rate control coding apparatus which and to a recordingmedium on which information generated by this variable transfer ratecontrol coding apparatus is recorded.

Further, it is another object of the present invention to provide avariable transfer rate moving picture information reproducing apparatuswhich can reproduce variable transfer rate moving picture information(namely, moving picture information coded at a variable transfer ratechanging every prescribed time period and recorded on a recordingmedium) from the recording medium at the time of decoding thereofwithout changing the relative speed between the recording medium and thereproducing head and to provide a recording medium suitable for therecording of the variable transfer rate moving picture information bythe reproducing apparatus.

SUMMARY OF THE INVENTION

To achieve the foregoing object, in accordance with an aspect of thepresent invention, there is provided a variable transfer rate controlcoding apparatus which can distribute codes of an amount most suitableto the contents of a moving picture to be recorded on a recording mediumand to a recording medium by obtaining an amount of codes to betemporarily generated to each unit period of time by a temporary ortentative coding, and then storing a value of the temporary amount ofcodes to be generated in each unit period of time (hereunder sometimesreferred so as a temporary transfer rate), and setting a target value ofan amount (hereunder sometimes referred to as a transfer rate) of codesto be sent in each unit period of time (namely, setting a targettransfer rate) from a total of the temporary transfer rates and therecordable capacity of the recording medium and next performing anactual coding (hereunder sometimes referred to as a real coding)according to the target transfer rates. Moreover, there is provided arecording medium on which information is recorded by this variabletransfer rate coding apparatus.

Namely, the variable transfer rate coding apparatus for performing acoding on a moving picture signal, which comprises temporary codingmeans for obtaining a temporary transfer rate representing an amount ofcodes to be generated in each unit period of time from the movingpicture signal and target transfer rate setting means for setting atarget transfer rate corresponding to each unit period of time from thetemporary transfer rate in such a manner that a total amount of codesgenerated from the moving picture signal is equal to a predeterminedvalue. Thus, a coding of the moving picture signal is effected bycontrolling an amount of generated codes in accordance with the targettransfer rate corresponding to each unit period of time.

Further, the target rate setting means of a preferred embodiment(namely, a variable transfer rate control coding apparatus) of thepresent invention is provided with a transfer rate converting devicewhich converts the temporary transfer rate corresponding to each unitperiod of time into the target transfer rate corresponding to each unitperiod of time by making increase in the target transfer rate be lessthan increase in the corresponding temporary transfer rate and limitingthe maximum value of the target transfer rate to a predeterminedconstant value.

Furthermore, in a preferred embodiment (namely, a recording medium) ofthe present invention, the transfer rate of the moving pictureinformation recorded thereon is not constant, and an amount of codesrecorded thereon and generated from the entire moving picture is made tobe nearly equal to the available (or recordable) capacity of therecording medium.

Thus, as described above, in case of the variable transfer rate controlcoding apparatus, an amount of codes to be temporarily generated in eachunit period of time is obtained by a temporary coding, and thereafter atarget value of an amount (hereunder sometimes referred to as a transferrate) of codes to be sent in each unit period of time (namely, setting atarget transfer rate) is set from a total of the temporary transferrates and the recordable capacity of the recording medium and finally,an actual coding is performed according to the target transfer rate. Asthe result, an amount of codes corresponding to a portion of an image,the quantization of which would be excessively fine in case of theconventional coding apparatus, becomes small and an amount of codescorresponding to another portion of an image, the picture quality ofwhich would be degraded by coarse quantization in case of theconventional coding apparatus, becomes large.

Thus, in accordance with the present invention, amounts of codes aresuitably distributed to portions of the image according to the contentsof information representing the portions, and moreover the picturequality is improved. Furthermore, the target transfer rate correspondingto each unit period of time is set in such a manner that a total amountof codes is constant. Therefore, by controlling a coding according tothe target transfer rate, even if the length or duration of a movingpicture is changed, all codes are recorded on the recording mediumwithout waste thereof. Further, in accordance with the presentinvention, fluctuation in quantized value becomes small and as aconsequence, change in picture quality due to the control of a codingbecomes also small.

Especially, regarding an inter-image prediction coding, an amount ofdata generated corresponding to a portion, in which there is no motion,of a picture is small. Consequently, the picture quality is improvedsharply.

Further, although the transfer rate may vary with unit periods of time,the transfer rate is unchanged within each unit period of time. Thus,the variable transfer rate control coding and decoding apparatuses ofthe present invention have good compatibilities with fixed transfer ratecoding and decoding apparatuses, respectively. Further, the formers canbe realized by adding systems each for controlling a total amount ofcodes to the latter, respectively.

Moreover, if the variable transfer rate control coding apparatus of thepresent invention and the conventional coding apparatus use a recordingmedium of same recording capacity and obtain same picture quality, thevariable transfer rate control coding apparatus of the present inventioncan record longer than the conventional coding apparatus does.

Furthermore, the recording medium of the present invention is a mediumon which image information generated by the variable transfer ratecontrol coding apparatus of the present invention is recorded. Each timewhen a unit period of time passes, the transfer rate is controlled orregulated according to the contents of a portion, which corresponds to aunit period of time, of information to be recorded, the total amount ofcodes obtained from the information and the recording capacity of therecording medium. Thus, information is recorded on the full recordingcapacity of the recording medium. Consequently, the picture quality of amoving picture reproduced from the recording medium is much better thanthat of a moving picture reproduced from codes recorded by theconventional coding apparatus employing a fixed transfer rate.

As described above, the variable transfer rate control coding apparatusand the recording medium of the present invention have excellent effectsin practical use.

Further, in accordance with another aspect of the present invention,there is provided a variable transfer rate information recording medium,on which moving picture information coded by changing the transfer rateis recorded and on which reading operation control information is alsorecorded in a multiplex recording manner. The reading operation controlinformation is used for directing information reading means of areproducing apparatus to read information or to stand by instead ofreading the information, when reproducing information from thisrecording medium.

Moreover, in accordance with a further aspect of the present invention,there is provided a variable transfer rate information recording medium,on which moving picture information coded by changing the transfer rateis recorded and on which information representing an amount of codesgenerated from a portion corresponding to a unit period of time of amoving picture is also recorded in a multiplex recording manner.

Furthermore, in accordance with still another aspect of the presentinvention, there is provided a variable transfer rate informationreproducing apparatus for reproducing moving picture information codedwhile changing a transfer rate every predetermined period of time andrecorded on a recording medium, which apparatus is provided withinformation reading means for intermittently reading informationaccording to an amount of information necessary for decoding eachpredetermined period of time. When information should not be read, theinformation reading means ceases to read information and stands bywithout changing the relative speed between a reproducing head and therecording medium. Further, in case that it is not necessary to readinformation, the information reading means reads the read informationagain and thereafter discards unnecessary information.

Moreover, in accordance with yet another aspect of the presentinvention, there is provided a variable transfer rate informationreproducing apparatus for reproducing moving picture information codedwhile changing a transfer rate every predetermined period of time andrecorded on a recording medium, which apparatus is provided with adecoding buffer for temporarily storing read information, buffer meansfor outputting an occupancy of the decoding buffer, reading controllerfor outputting reading control information according to the occupancy ofthe decoding buffer, and information reading mean which occasionallydoes not read information but stands by according to the reading controlinformation.

Furthermore, in accordance with another aspect of the present invention,there is provided a variable transfer rate information reproducingapparatus for reproducing information from a recording medium on whichreading operation control information for controlling the informationreading means to read information or stands by instead of readinginformation and moving picture information are recorded in a multiplexrecording manner, which apparatus is provided with control informationseparation means for detecting the reading operation controlinformation, and in which information reading means occasionally doesnot read information but stands by according to the reading operationcontrol information.

Further, in accordance with a further aspect of the present invention,there is provided a variable transfer rate information reproducingapparatus for reproducing information from a recording medium on whichinformation representing a transfer rate of a moving picture signalcorresponding to each unit period of time and moving picture informationcoded while changing the transfer rate thereof every unit period of timeare recorded in a multiplex recording manner, which apparatus isprovided with transfer rate information separation means for detectingcode amount information representing a transfer rate of the movingpicture signal corresponding to each unit period of time, readingoperation controller for outputting control information according to thecode amount information and information reading means which occasionallydoes not read but stands by according to the reading operation controlinformation.

Additionally, in accordance with a still further aspect of the presentinvention, there is provided a variable transfer rate informationreproducing apparatus for reproducing moving picture information from arecording medium on which the moving picture information coded whilechanging a transfer rate every unit period of time is recorded as apacket of information, which apparatus is provided with packet codeamount detector for detecting an amount of the packet of readinformation, reading operation controller for outputting readingoperation control information according to an amount of informationcorresponding to the packet and information reading means which ceasesto read information and stands by according to the reading operationcontrol information.

Further, in accordance with a yet further aspect of the presentinvention, there is provided a variable transfer rate informationreproducing apparatus for reproducing information on a recording mediumon which fixed-transfer-rate information coded while fixing a transferrate and moving picture information coded while changing a transfer rateevery predetermined period of time are recorded in a multiplex recordingmanner, which apparatus is provided with a fixed-transfer-rate detectorfor detecting an amount of codes generated from the information for theperiod of the predetermined length, information reading means forreading information recorded on the recording means and readingoperation control means for controlling the information reading means insuch a manner that the amount of codes generated in each period of thepredetermined length becomes constant. The information reading meansoccasionally does not read information and stands by according to thereading control information.

As described above, on the recording medium of the present invention,what is called variable transfer rate information obtained bycontrolling a transfer rate every period of the predetermined length isrecorded. Further, reading control information for controlling thereproducing apparatus to read information or stands by instead ofreading information and information indicating an amount of codesrepresenting the variable transfer rate information are also recordedthereon in a multiplex recording manner.

In case of the variable transfer rate information reproducing apparatusof the present invention, the variable transfer rate informationrecorded on the recording medium is ready by the information readingmeans provided in the reproducing apparatus.

Incidentally, information is read by the information reading means fromthe recording medium at a predetermined rate (namely, information of apredetermined amount is read in a period of predetermined length).

The read information is stored in the decoding buffer. Thereafter,information of an amount necessary for decoding is outputted from thisbuffer. In case of decoding codes generated from fixed-transfer-rateinformation, the amount necessary for decoding is constant amountcorresponding to a period of the predetermined length. In contrast, incase of decoding codes generated from variable transfer rateinformation, the amount necessary for decoding varies every period ofthe predetermined length.

Further, an amount of information stored in the buffer, as well as theoccupancy of the buffer, changes according not only to the decoding rate(or the reading rate) but to whether information is read from therecording medium (or whether a reading operation is ceased and theapparatus stands by).

Moreover, the information reading means is controlled to readinformation or cease to read and stand by according to the occupancy ofthe buffer and the control information recorded on the recording mediumin a multiplex recording manner.

As described above, the variable transfer rate information reproducingapparatus of the present invention is provided with the informationreading means for intermittently reading information according to theamount of information necessary for decoding codes generated from themoving picture every period of the predetermined length. Further, thisinformation reading means is controlled according to the occupancy ofthe buffer and the amount of codes generated from information in aperiod of the predetermined length to read information from therecording medium or to stand by without reading information. Thereby,the information coded at a variable transfer rate changing everypredetermined period of time and recorded on the recording medium can bereproduced without changing the relative speed between the recordingmedium and the reproducing head.

Moreover, in case of the reproducing apparatus of the present invention,reading operation control information for controlling the informationreading means and the information concerning the amount of codesgenerated in each period of the predetermined length are recorded on therecording medium in a multiplex manner and are thereafter used at thetime of reproduction. This facilitates a control processing of theinformation reading means. Consequently, information recorded atvariable transfer rate can be reproduced by utilizing a buffer ofrelatively small capacity and a small delay time.

As stated above, the variable transfer rate information reproducingapparatus and the recording medium used therein of the present inventionhave excellent effects in practical use.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, objects and advantages of the present invention willbecome apparatus from the following description of preferred embodimentswith reference to the drawings in which like reference charactersdesignate like or corresponding parts throughout several views, and inwhich:

FIG. 1 is a schematic block diagram for illustrating the configurationof a conventional image coding apparatus;

FIG. 2 is a diagram for illustrating the manner of quantization control;

FIG. 3 is a schematic block diagram for illustrating the configurationof a conventional decoding apparatus;

FIG. 4 is a schematic block diagram for illustrating the configurationof a variable transfer rate control coding apparatus embodying (namely,an embodiment of) the present invention;

FIG. 5 is a schematic block diagram for illustrating the configurationof a code amount controller of the embodiment of the present invention;

FIG. 6 is a graph for showing the conversion characteristics betweentemporary transfer rates and target transfer rates corresponding to eachunit period of time;

FIGS. 7(A) and 7(B) are diagrams for illustrating data streams (or codesequences) recorded on a recording medium;

FIG. 8 is a schematic block diagram for illustrating the configurationof a variable transfer rate decoding apparatus embodying the presentinvention for decoding codes generated by the variable transfer ratecontrol coding apparatus of FIG. 4;

FIG. 9 is a schematic block diagram for illustrating the configurationof a first example of a variable transfer rate information reproducingapparatus embodying the present invention;

FIG. 10 is a graph for illustrating a reading operation control effectedby the first example of the variable transfer rate informationreproducing apparatus of FIG. 9;

FIGS. 11(a), 11(b) and 11(c) are diagrams for showing examples ofrecording formats employed by a variable transfer rate informationrecording medium embodying the present invention;

FIG. 12 is a schematic block diagram for illustrating the configurationof a second example of a variable transfer rate information reproducingapparatus embodying the present invention;

FIG. 13 is a diagram for showing an example of a recording formatemployed by a recording medium used by the reproducing apparatus of FIG.12;

FIG. 14 is a schematic block diagram for illustrating the configurationof a third example of a variable transfer rate information reproducingapparatus embodying the present invention;

FIGS. 15(a) and 15(b) are diagrams each for showing an example of arecording format employed by a recording medium used by the reproducingapparatus of FIG. 14;

FIG. 16 is a schematic block diagram for illustrating the configurationof a fourth example of a variable transfer rate information reproducingapparatus embodying the present invention;

FIG. 17 is a schematic block diagram for illustrating the configurationof a fifth example of a variable transfer rate information reproducingapparatus embodying the present invention; and

FIG. 18 is a diagram for showing an example of a recording formatemployed by a recording medium used by the reproducing apparatus of FIG.17.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail by referring to the accompanying drawings.

FIG. 4 is a schematic block diagram for illustrating the configurationof a variable transfer rate control coding apparatus embodying thepresent invention.

In this figure, like reference characters designate like orcorresponding parts of the conventional apparatus of FIG. 1.

Principal differences between the coding apparatuses of FIGS. 1 and 4(namely, composing elements of FIG. 4 which are not contained in FIG. 1)are a VTR 1, selectors 8 and 9, a temporary code amount counter 16, acode amount controller 17, a target transfer rate setting device 18 anda temporary transfer rate memory 19.

Hereinafter, a coding performed in this variable transfer rate controlcoding apparatus will be described in detail by referring to FIG. 4.

A coding is performed on a same moving picture signal two times. Atfirst time, a coding process is performed for effecting a temporarycoding for setting a target transfer rate corresponding to each unitperiod of time. At second time, another coding process is performed foreffecting an actual coding (or a real coding). Therefore, in case of acoding apparatus which performs a coding at the same speed as therunning speed of a moving picture, the processing time required forperforming the coding process twice is nearly two times the running timeof the moving picture.

A method for fixing a total amount of codes to a constant value anddistributing the amounts of codes by performing such a feed forwardprocessing has been proposed by the inventor of the present invention.Basic ideas employed in this method are described in previous JapanesePatent Applications (see, for example, the Japanese Unexamined PatentPublication (Kokai Tokkyo Koho) Official Gazette Nos. S63-151225,H2-194734 and H3-263927).

An object to be processed by the apparatus of the present invention is amoving picture signal. Further, the activity is not used as an estimateof an amount of codes. Moreover, the apparatus of the present inventionperforms a coding, which is the same as a real coding, and uses anoutput coded by a variable length coding. In contrast, in cases of theapparatuses of the previous applications, a unit period (hereundersometimes referred to as a target-transfer-rate setting unit period), towhich a target transfer rate is set correspondingly, is equal to a unitperiod (hereunder sometimes referred to as a control-operation unitperiod), to which a control operation is effected correspondingly.However, in case of the apparatus of the present invention, atarget-transfer-rate setting unit is equal to a predetermined unitperiod of time and a control operation unit period is less than thepredetermined unit period of time. Further, a target transfer rate isset in such a manner to become less than a corresponding temporarytransfer rate and to be less than a predetermined upper limit as will bedescribed.

When performing a temporary coding, quantization control is notperformed according to the occupancy of a buffer. Instead, a transferrate corresponding to each unit period of time is fixed to apredetermined value and then a temporary amount of codes correspondingto each unit period of time (namely, a temporary transfer rate) isobtained. Upon completion of this processing, the conversioncharacteristics between the temporary transfer rate and thecorresponding target transfer rate are determined from the total amountof codes and the capacity of the recording medium correspondingly toeach unit period of time.

When performing an actual coding (namely, a real coding), the targettransfer rate is established from the corresponding temporary transferrate and the conversion characteristics every unit period of time.Moreover, the real coding is controlled according to the occupancy ofthe buffer and the target rates. Incidentally, the target transfer rateis set in such a fashion that moving picture signals to be recorded arejust stored in the recordable area of the recording medium. Thus, solong as the buffer does not overflow, the total amount of codes obtainedas the result becomes adapted to the recording medium.

At least, during each unit period of time, the transfer rate is notchanged and is kept constant. Usually, a buffer 10 has capacitycorresponding to an amount of codes generated in a period of 0.2 to 0.3second. Further, instantaneous change in amount of codes is absorbed bythe buffer 10. Thus, the unit period of time is set to be a littlelonger than the length of a short period in which the change in amountof codes occurs. Namely, it is preferable that the unit period of timeis set as adapted to change of a long period. For example, the unitperiod of time is set to be 0.5 to 0.1 second.

Incidentally, in cases of the apparatus of the previous applications,simple activity is used when estimating an amount of codes. In contrast,in case of this embodiment, a nearly same coding is performed two times.Thus, there is no necessity of simplifying a coding process. Therefore,similarly as in case of the real coding, a variable length coding isperformed as the temporary coding. Consequently, an exact amount ofgenerated codes can be obtained from an output signal representing aresult of the coding.

Conversely, there has been proposed a method of using a plurality ofquantizers and variable length coders and estimating an amount of codesby effecting different types of quantization. In case of this method,what is called cyclic prediction is employed for performing a coding.Thus, differences in quantization influence a result of the prediction.Consequently, a precise amount of codes can not be obtained if aplurality of quantizers and a plurality of variable length coders arenot provided for the inter-image prediction or the like.

Next, a temporary coding means 30 of this embodiment will be describedin detail hereinbelow. The temporary coding means 30 is used to obtainthe temporary transfer rate for transferring the moving picture signal.

As showing in FIG. 4, an image signal outputted from the VTR 1 isinputted to the prediction subtracter 2 and the activity detector 4. Incase of this embodiment, the same image signal is supplied to a codingportion two times. Therefore, all image signals before coded arerecorded on a mass image recording medium such as VTR. For instance, amemory element as optical disk and a hard disk drive (HDD) which havesufficient capacity may be employed as the mass image recording medium.

In case of the apparatus of FIG. 4, a basic coding process is similarlyto that of the conventional apparatus. First, a prediction signalsupplied from the inter-image predictor 13 is subtracted by theprediction subtracter 2 from the image signal outputted from the VTR 1.Then, a signal representing a result of this subtraction (namely, apredictive residual) is inputted to the DCT device 3. Thereafter, a DCToperation and a quantization operation are effected by the DCT device 3and the quantizer 6, respectively. Subsequently, this quantized signalis inputted to the variable length coder 7 and the local decoder 15.Information represented by the quantized signal is converted by thevariable length coder 7 into a compressed code. This compressed code isthen inputted to the selector 9.

At the time, an input to the selector 8 is switched to a terminal Athrough which a predetermined fixed value is inputted to thequantization controller 5 as the occupancy of the buffer. Thus thequantization is changed only by the activity corresponding to eachblock, which is inputted from the activity detector 4 to thequantization controller 5. Incidentally, the fixed value is set in sucha way that the image coded by using this fixed value has sufficientpicture quality.

On the other hand, in the local decoder 15, the code is decoded toproduce a reproduced prediction residual signal. This reproducedprediction residual signal is then inputted to the adder 14 whereuponthe prediction signal inputted from the inter-image predictor 13 isadded to the reproduced prediction residual signal. Then, a reproducedimage signal represented a result of this addition is inputted to theinter-image predictor 13 whereupon an inter-frame prediction signal isgenerated from the reproduced image signal. Subsequently, theinter-frame prediction signal is supplied to the prediction subtracter 2and the adder 14.

In case of the apparatus of FIG. 4, at time of the first coding, anoutput of the variable length coder 7 is inputted to the temporary codeamount container 16 through the selector 9. Further, an amount of codesgenerated in each unit period of time is counted by the temporary codeamount counter 16 and a signal representing the count (namely, theamount of codes generated in each unit period of time) is then outputtedtherefrom.

Next, a target transfer rate setting means 40 will be described indetail hereinbelow. This target transfer rate setting means 40 is usedto set a target transfer rate from the temporary amount of codes eachunit period of time in such a manner that a total of amounts of codesgenerated from the moving picture signals becomes a predetermined value.

The temporary transfer rate outputted from the temporary code amountcounter 16 is inputted to the code amount controller 17 and thetemporary transfer rate memory 19. In the temporary transfer rate memory19, all of the transfer rates respectively corresponding to unit periodsof time, which are used again in the actual coding (real coding), arestored.

For instance, in case where a moving picture, the running time of whichis 1 hour, is represented by a set of data corresponding to 1 second,the amount or number of data to be stored is 3600. The code amountcontroller 17, whose configuration is shown in FIG. 5, is used todetermine the conversion characteristics between the temporary transferrates and the target transfer rates.

FIG. 5 is a schematic block diagram for illustrating the configurationof the code amount controller 17 of this embodiment.

As shown in this figure, the temporary transfer rate inputted from thetemporary transfer rate input terminal 51 is converted by n transferrate converting devices (hereunder sometimes referred to simply asconverters) 52, 53, 54, . . . whose conversion characteristics aredifferent from one another. Thereafter, the transfer rates respectivelycorresponding to the conversion characteristics are accumulated by theaccumulation adders 55, 56, . . . 57 over the entire running time of themoving picture. Thus the total amount of codes, which are generated fromthe entire picture and correspond to each of the converters, isobtained.

Upon completion of the temporary coding, the total amounts of codescorresponding to the transfer rate converting devices (or converters)are inputted to comparators 58, 59, . . . 60, respectively, whereuponthe inputted total amounts of codes are target total amounts of codesset from the recordable capacity of the recording medium. Then, outputsof the comparators are inputted to a judgment device 61 for makingcomparisons between each pair of the output of the comparators. Thejudgement device 61 determines and selects the conversion characteristiccorresponding to the total amount of codes which is less than the targettotal amount of codes but is greater than any of the total amounts ofcodes corresponding to the other conversion characteristics. Then,information representing the selected conversion characteristic isinputted from the conversion characteristic information output terminal62 to the target buffer rate setting device 18 of FIG. 4. FIG. 6 showsthe conversion characteristics corresponding to the converters 1 to n.

Namely, FIG. 6 is a graph for showing the conversion characteristicsbetween the temporary transfer rates and the target transfer ratescorresponding to each unit period of time. As shown in this figure, theupper limit (Rmax) to the outputs of the transfer rate convertingdevices is first determined. This is due to the facts that there is anupper limit to the processing ability (or throughputs) of the recordingmedium and the decoder and that the maximum transfer rate is determinedaccording to this upper limit to the throughputs. Therefore, althoughthe variable transfer rates are employed, the maximum target transferrate is a fixed value.

As shown in this figure, for example, logarithmic characteristics areemployed as the conversion characteristics, by which change in eachtarget transfer rate is compressed or suppressed throughout incomparison with change in each temporary transfer rate, corresponding tothe transfer rate converting devices. Namely, each target transfer rateis controlled as gently increases. In case of a portion of the picture,which portion corresponds to a small temporary amount of codescorresponding to each unit period of time, degradation in visual picturequality is conspicuous. Therefore, the amount of codes is somewhatincreased.

The conversion characteristics between the temporary transfer rate X andthe target transfer rate R are given by, for instance, the followingequations:

R=K*LOG(Y*X);

or

R=K*X^(Z)

wherein K and Y are positive numbers and Z is a positive number lessthan 1. The conversion characteristics can be changed by changing thevalues of Y and Z.

Namely, when the target transfer rate corresponding to each unit periodof time is obtained by converting the temporary transfer ratecorresponding to each unit period of time, the conversion is effected bymaking a ratio of increase in the target transfer rate to correspondingincrease in the temporary transfer rate less than 1 and limiting themaximum value of the target transfer rate to a constant value.

The larger the number n of kinds of the conversion characteristicsbecomes, the more precise the selected conversion characteristicsbecome. Thus, waste in capacity of the recording medium becomes smaller.

Incidentally, in case of the code amount controller 17 of FIG. 5, thetransfer rate converting devices, the accumulation adders and thecomparators are placed in parallel with one another as illustrated inthis figure and operate in parallel with the temporary coding. However,the apparatus may employ a serial processing instead of such a parallelprocessing.

In case of employing a serial processing, the code amount controller hasonly one transfer rate converting device, one accumulation adder and onecomparator, which are as illustrated in FIG. 5. In this case, after thetemporary coding is finished and before the real coding is performed,the total amounts of codes corresponding to various conversioncharacteristics are calculated from the data stored in the temporarytransfer rate memory 19. As a consequence, a conversion characteristicmost suitable for calculating the target transfer rate is selected.Further, information representing the selected conversion characteristicis outputted. Such a serial processing is described in, for example, theJapanese Unexamined Patent Publication (Tokkyo Kokai Koho) OfficialGazette No. H2-417572.

Next, the coding means for performing an actual coding (namely, a realcoding) will be described in detail hereinbelow. This coding means isused to perform a coding by controlling an amount of codes in accordancewith the target transfer rate corresponding to a unit period of time.

In case of the apparatus of FIG. 4, the same image signal as used in thetemporary coding is outputted from the VTR 1. Then, a coding similar tothe temporary coding is performed. Basically, manners of operation is ofthe prediction subtracter 2, the DCT device 3, the activity 4, thequantization controller 5, the quantizer 6, the variable length coder 7,the inter-image predictor 13, the adder 14 and the local decoder 15 aresimilar to those of the operation of the corresponding elements in caseof performing the temporary coding. However, the contents of theoperation of these elements in case of performing the real coding aredifferent from those of the operations of these elements in case ofperforming the temporary coding.

When performing the real coding, an output of the variable length coder7 is applied to the buffer 10 through the selector 9. Further, variationin amount of generated codes, which variation is of a short period, isabsorbed by the buffer 10. Codes are outputted from the buffer 10through the code output terminal 11 to the decoder.

Furthermore, a reading rate for reading a code from the buffer 10 iscontrolled by a value supplied from the target transfer rate settingdevice 18 every unit period time. Thus, the amount of codes outputtedfrom the buffer 10 changes each unit period of time. In the targettransfer rate setting device 18, the temporary transfer rate inputtedfrom the temporary transfer rate memory 19 every unit period of time isconverted according to the conversion characteristics inputted from thecode amount controller 17 and thus the target transfer rate isestablished.

On the other hand, information representing the occupancy of the buffer10 is inputted to the quantization controller 5 through the selector 8.

Further, the quantization step width is controlled by the quantizationcontroller 5 according to the activity and the filling rate of thebuffer. In case of such control, differently from the conventionalapparatus, variation in amount of generated codes, which variation is ofa long period, is absorbed by utilizing a variable transfer rate everyunit period of time. Thus only local variation thereof is absorbed.Consequently, the possibility of an occurrence of an overflow becomeslow.

Incidentally, in case where there is no need of utilizing a fixedtransfer rate for an output of the buffer, the buffer is treated as avirtual one and thus an output of the variable length coder 7 isdirectly outputted.

Next, it will be described hereinbelow by referring to FIGS. 7(A) and7(B) how data streams coding by the coding apparatus are recorded by theapparatus of the present invention and the conventional apparatus.

FIGS. 7(A) and 7(B) are diagrams for illustrating the data streams (orcode sequences) recorded on the recording medium.

In these figures, numerals designate numbers of unit periods of time.Practically, there are unit periods, the number of which is far largerthan the number of unit periods illustrated in these figures. In case ofthe conventional apparatus, when the data stream is recorded on therecording medium, the amount of data of a portion of the data streamcorresponding to a unit period is constant as illustrated in FIG. 7(A).As the result, an open space is generated in the recording medium. Incontrast, in case of the embodiment of the present invention, the amountof codes of the data stream changes every unit period of time asillustrated in FIG. 7(B). Moreover, no space occurs in the recordingmedium because the total amount of codes is controlled.

Next, a variable transfer rate decoding apparatus of the presentinvention will be described hereinbelow by referring to FIG. 8.

FIG. 8 is a schematic block diagram for illustrating the configurationof the variable transfer rate decoding apparatus of the presentinvention for decoding codes generated by the variable transfer ratecontrol coding apparatus of FIG. 4.

In this figure, like reference characters designate like orcorresponding elements (namely, elements having the same functions) ofthe conventional apparatus of FIG. 3. The decoding apparatus of FIG. 8is different from the conventional decoding apparatus of FIG. 3 in thatthe transfer rate is inputted to the buffer 21.

The codes inputted from the code input terminal 20 are outputted fromthe buffer 21 to the variable length decoder 22 in synchronization withthe operation performed in the device 22. Further, a speed of writingthe transfer ratio to the buffer 21 is controlled according to rateinformation inputted from the transfer rate input terminal 27 every unitperiod of time in such a manner to be adapted to the transfer rate ofthe inputted code.

Turning to FIG. 9, there is shown a schematic block diagram forillustrating the configuration of a first example of a variable transferrate information reproducing apparatus embodying the present invention.

In case of the apparatus of this figure, information coded at a variabletransfer rate changing every predetermined period of time and recordedon the recording medium is read intermittently by an information readingmeans 94 from the recording medium and subsequently is inputted tobuffer means 95A having a decoding buffer for decoding. Further,information outputted intermittently from information reading means 94is [Moreover,] written to the buffer means 95A. Moreover, theinformation is outputted therefrom to a demultiplexer 96 when theinformation is necessary for decoding.

In the demultiplexer 96, audio information and image information areseparated. Then, the audio information and the image information areinputted to an audio detector 92 and an image decoder 97, respectively.Further, the audio information and the image information are decoded bythe audio decoder 92 and the image decoder 97, respectively. Moreover, areproduced audio and a reproduced image are outputted from areproduction audio output terminal 93 and a reproduced image outputterminal 98.

On the other hand, information representing the occupancy of the buffer,which information is outputted from the buffer means 95A, is fed to areading operation controller 99. At that time, the buffer means 95Abecomes almost empty when an amount of written information is small incomparison with an amount of information required for decoding. Further,the buffer means 95A becomes nearly full of information when an amountof information written thereto is larger than an amount of informationused for decoding.

Then, reading operation control information is outputted from thereading operation controller 99 to the information reading means 94according to the state of the buffer means 95A. Namely, when the bufferof the buffer means 95A is nearly empty, reading operation controlinformation is outputted to initiate a reading operation or to continueto performed a reading operation. Further, when the buffer is nearlyfull of information, the reading operation control information isoutputted to control the information reading means to cease a readingoperation and stand by.

Next, a method for controlling the information reading means 94 will bedescribed concretely hereinbelow.

A reading of information by the information reading means 94 from therecording medium is performed by using, for example, a period of onerevolution of a disk as a unit period of time.

Further, even in case where information is not read by the informationreading means 94 from the recording medium at present time and on theother hand, information is read from the buffer means at the maximumrate for decoding, a reading operation of the information reading means94 is controlled is such a way that the buffer of the buffer means doesnot become empty until the next reading operation is started.

For example, in case where an amount of codes read from the recordingmedium during a period of the predetermined length (hereunder sometimesreferred to as a reading rate) is equal to a maximum amount of codesrequired for decoding during a period of the predetermined length(hereunder sometimes referred to as a decoding rate), the buffer of thebuffer means 95A needs capacity which is a little larger than an amountof information read two times. Further, the information reading means 94is controlled in such a manner that if a recording area, on whichinformation left in the buffer is recorded, is less than half of therecordable area of the buffer, the reading operation is kept performedand that if the recording area, on which information left in the bufferis recorded, is equal to or greater than half of the recordable area ofthe buffer, the reading operation is ceased and the information readingmeans stands by.

A more practical manner of such control is illustrated in FIG. 10.

FIG. 10 is a graph for illustrating a manner of such reading control andillustrates the relation among the decoding rate, the reading rate andthe occupancy of the buffer.

As illustrated in this figure, the decoding rate varies everypredetermined period Td. Further, information is read from the recordingmedium intermittently at a predetermined reading rate. It is controlledevery predetermined period Tr whether or not a reading of information isperformed.

In a period between the moments t13 and t14, the decoding rate has amaximum value Rmax. Further, the value of the reading rate is Rmax.Thus, during this period, the occupancy of the buffer does not change.

In contrast, in a period between the moments t1 and t2, the reading rateis greater than the decoding rate. Thus, during this period, theoccupancy of the buffer increases. At a moment t2 at which a period oftime Tr has passed since a reading operation is commenced at the momentt1, the occupancy of the buffer is larger than a level indicated by thedashed central line K (namely, half of the capacity of the buffer).Thus, the reading operation is stopped. After the moment t2, theoccupancy of the buffer decreases and becomes equal to the levelindicted by the central line K at a moment t3.

At a moment t4 when a period 2Tr has passed since the moment t2 at whichthe reading operation is ceased at the precedent time, the occupancy ofthe buffer is less than ½. Thus, the reading operation is resumed.

In case of this example, the moment when the decoding rate changes issynchronized with the moment at which the reading operation is commencedor ceased as illustrated in this figure. However, it is not necessary tosynchronize former moment with the latter moment.

Further, the information reading means 94 of FIG. 9 performs aninformation reading operation in accordance with the reading operationcontrol information sent from the reading operation controller 99.However, is practical method for controlling the information readingmeans to keep reading information from the recording medium or to ceasereading such information and stand by varies with the kind of therecording medium employed.

In case of employing a disk medium, the practical method for controllingthe reading operation varies with the manner of controlling a trackingof a reproducing head. For example, in case of employing what is calleda disk of the spiral type in which information track is continuous, ausual reading operation is continuously performed when an informationreading operation is kept performed. In contrast, when the informationreading operation should be stopped and the apparatus should stand by,the reproducing head is skipped to the precedent track and a tracing isrepeatedly performed on the track corresponding to an already read partof information. Thus the apparatus falls into a stand-by state.

In contrast with this, in case of employing what is called a disk of theconcentric circle type in which information track is closed like acircle, the apparatus falls into a stand-by state by repeatedlyperforming a tracing on the track corresponding to am already read partof information. Then, the reproducing head is skipped to the subsequenttrack to read information recorded on the next track.

Meanwhile, in case of a VTR having what is called a rotary drum,information tracks are distributed discontinuously on tape. Thus, afterinformation is once read from the track, the tape or reproducing head ismoved. Further, a tracing is repeatedly performed on the portion whichhas been already read. Thus the apparatus is put into a stand-by state.Moreover, the reproducing head or the tape is shifted in such a mannerthat the reproducing head is set on the subsequent track. Thusinformation recorded on the next track is read.

Information recorded on the recording medium at a variable transfer ratecan be realized by controlling the information reading means to keepreading information or stand by without changing the number ofrevolutions of the disk or drum, namely, without changing the relativespeed between the reproducing head and the recording medium as describedabove.

Further, in the stand-by state, the reproducing head may repeatedly readinformation recorded on the same track and outputs the read information.Further, unnecessary information may be discarded later. In this case,information is read in a narrow sense. However, substantially,information to be read is not read. In the following description, theexpression “does not read and stands by” means “does not readsubstantially and stands by”, precisely speaking.

FIGS. 11(a), 11(b) and 11(c) are diagrams for showing examples ofrecording formats employed by a variable transfer rate informationrecording medium according to the present invention.

The formats of FIGS. 11(a), 11(b) and 11(c) are the recording formats tobe used for recording information on the variable transfer rateinformation recording medium of the present invention (incidentally, therecording formats to be used for the recording medium of the compactdisk read-only memory (CD-ROM) type are shown in these figures).

In these cases, the recording area of the recording medium ispartitioned into sectors having a predetermined number of bytes asillustrated in FIG. 11(a). Each sector consists of a sector header area,on which management information concerning synchronization signals andsector addresses is recorded, and a data area, on which imageinformation and audio information are recorded.

In case that data (or information) recorded on the data area of FIG.11(a) are read from the recording medium in succession. The read dataare an audio header, audio data, image header and image data which arerecorded in this order as illustrated in FIG. 11(b). Further, asillustrated in FIG. 11(c), a synchronization code is recorded on aleading address of each of the headers.

FIG. 12 is a schematic block diagram for illustrating the configurationof a second example of a variable transfer rate information reproducingapparatus according to the present invention.

In this figure, same reference characters designate same orcorresponding elements (namely, elements having the same functions) ofthe apparatus of FIG. 9. For simplicity of description, the explanationof these elements is omitted herein.

Differently from the apparatus of FIG. 9, the apparatus of FIG. 12 doesnot have the reading controller 9 but is provided with controlinformation separation device 121. In case of the example, readingoperation control information used for controlling information readingmeans is preliminarily set in an encoder (namely, the coding apparatus).Further, the reading operation control information is preliminarilyrecorded on the recording medium in a multiplex recording manner.

In case of the apparatus of FIG. 12, information read from the recordingmedium by information reading means 94 is inputted to buffer means 95and control information separation device 121.

Operations of the demultiplexer 96, the audio decoder 92 and the imagedecoder 97, which follow the buffer means 95, are similar to those ofthe same elements of the first example of FIG. 9. Thus reproduced audioand image, which are decoded, are outputted from the reproduced audiooutput terminal 93 and the reproduced image output terminal 98,respectively.

On the other hand, the control information separation device 121 detectsthe synchronization code from an output of the information reading means94 and separates the reading operation control information. Theseparated information is inputted to the information reading means 94therefrom. In the information reading means 94, it is determinedaccording to the reading operation control information whether the means94 keeps reading information from the recording medium or stands by.

In this way, the reading operation control information is recorded onthe recording medium in a multiplex recording manner. When reproducingthe recorded information, the information reading means 94 is controlledaccording to the reading operation control information. This is rationaland results in that the processing can be easily performed in thedecoder or decoding apparatus. However, the delay time or the like ofthe control processing effected in the information reading means shouldbe definite.

Incidentally, the control information is recorded in the sector headeror the audio and image headers of the recording medium. Incidentally, inthe recording medium, a control header and a control information areamay be provided for recording the control information.

FIG. 13 is a diagram for showing an example of the recording formatemployed by the recording medium used by the reproducing apparatus ofFIG. 12.

FIG. 14 is a schematic block diagram for illustrating the configurationof a third example of the variable transfer rate information reproducingapparatus according to the present invention.

In this figure, same reference characters designate same orcorresponding composing elements (namely, elements having the samefunctions) of the apparatus of FIG. 9. For simplicity of description,the explanation of these composing elements is omitted herein.

The apparatus of FIG. 14 is different from the apparatus of FIG. 9 inthat the former apparatus is provided with a transfer rate separationdevice 131.

Information read from the recording medium and outputted by theinformation reading means 94 is inputted to the buffer means 95 andcontrol information separation device 131. Operations of the composingelements following the buffer means 95 are similar to those of the sameor corresponding elements of the second example of FIG. 12.

FIGS. 15(a) and 15(b) are diagrams each for showing an example of therecording format employed by the recording medium used by thereproducing apparatus of FIG. 14.

In case of the apparatus of FIG. 14, an information signal of the formatof FIG. 15(a) is outputted from the information reading means 94.Further, in the transfer rate separation device 131, the synchronizationcode corresponding to code amount information is detected from the audioheader and the image header. Then, amounts of codes B1 and B2corresponding to a period of the predetermined length, which arerecorded in these headers, respectively, are separated. Thus, thedecoding rate (namely, the transfer rate) corresponding to the period ofthe predetermined length is calculated, and the calculated decoding rateis inputted to the reading operation controller 99.

As is seen from FIG. 15(a), the code amount information represents anamount of codes (namely, decoding rate (or transfer rate)) required fordecoding of the recorded information following this code amountinformation and corresponding to the period of the predetermined lengththe audio code amount B1 and the image code amount B2 required forperforming a decoding every 100 milli-seconds (ms) (corresponding to 3frames in case of an NTSC (National Television System Committee)television are recorded on both of the headers.

Further, the code amount of information may be recorded by using theformat of FIG. 15(b). Namely, an audio header, audio data, an imageheader and image data are recorded as a packet of information. Further,a total value B1 of an audio code amount and an image code amount to bedecoded in a period, of, for instance, 100 ms is recorded in a packetheader.

In case of the apparatus of FIG. 14, the information reading means 94 iscontrolled by the reading operation controller 99. Thus the code amountto the read by the information reading means 94 is preliminary known. Onthe other hand, information representing an amount of codes needed forperforming a decoding is supplied from the transfer rate informationseparation device 131.

Thus, the future occupancy of the buffer means 95 can be predicted bythe reading operation controller 99 from an output of the readingoperation controller 99 and an output of the transfer rate informationseparation device 131. A control signal is supplied to the informationreading means 94 to prevent occurrences of an overflow and an underflowin the buffer means 95.

Namely, let Tr denote a unit period of time for performing a readingoperation by the information reading means 94 (see FIG. 10). Thepredicted occupancy of the buffer means 95 at a moment when the periodTr has passed since the present moment is calculated corresponding toeach of the cases that the reading operation is performed and that thereading operation is not performed. The reading means 94 is controlledin such a manner that the predicted occupancy is in the vicinity of thecentral line K of FIG. 10.

As can be seen from a comparison between the first example of FIG. 9 andthis example, in case of this example, the information reading means 94can be controlled faster and the necessary capacity of the buffer can bereduced because an amount of codes read from the buffer is knownpreliminarily.

Moreover, as can be seen from a comparison between the second example ofFIG. 10 and this example, in case of this example, the processing to beperformed in the decoder becomes somewhat complex but the informationreading means 94 can be controlled in such a manner to be fit for thethroughput thereof.

FIG. 16 is a schematic block diagram for illustrating the configurationof a fourth example of a variable transfer rate information reproducingapparatus according to the present invention.

In this figure, same reference characters designate same orcorresponding composing elements (namely, elements having the samefunctions) of the apparatus of FIG. 9. For simplicity of description,the explanation of these composing elements is omitted herein.

The example of FIG. 16 is different from the third example of FIG. 14 inthat the former example is provided with a packet code amount detector141 instead of the transfer rate separation device 131. Operations ofthe composing elements other than the packet code amount detector 141are similar to those of the same or corresponding elements of the thirdexample of FIG. 14.

In the packet code amount detector 141, a synchronization signalcorresponding to a packet is detected from an output of the informationreading means 94 and further an amount of codes of this packet ismeasured until a synchronization signal corresponding to the next packetis detected. In this way, an amount of codes of one packet is obtainedand is inputted to the reading operation controller 99. The format ofthis packet is similar to that of, for instance, FIG. 15(b). However, itis not necessary to record the amount of information of a packet in thepacket header.

Further, such a packet is established each period of the predeterminedlength (for example, 100 ms) required for a decoding. Thus an amount ofcodes of one packet is variable.

In case of the example of FIG. 16, the information reading means 94 iscontrolled by the reading operation controller 99. Thus the code amountto be read by the information reading means 94 is preliminarily known.On the other hand, information representing an amount of codes neededfor performing a decoding is supplied from the packet code amountdetector 141.

Thus, the reading operation controller 99 is controlled according to anoutput of the reading operation controller 99 and an output of thepacket code amount detector 141, similarly as in case of the thirdexample of FIG. 14.

As described above, in case of the third example, an amount ofinformation to be read is preliminarily known before a reading operationis performed. In contrast, in case of the fourth example, the result ofthe measurement effected by the packet code amount decoder 141represents an amount of codes concerning information already read.Thereby, the response to the control is a little slower than that incase of the third example. However, an amount of codes required fordecoding is known in a stage precedent to the buffer means 95.Therefore, the response is faster than that in case of the first examplein which the information reading means is controlled according to theoccupancy of the buffer.

FIG. 17 is a schematic block diagram for illustrating the configurationof the fifth example of the variable transfer rate informationreproducing apparatus according to the present invention.

In this figure, same reference characters designate same orcorresponding composing elements (namely, elements having the samefunctions) of the apparatus of FIG. 16. For simplicity of description,the explanation of these composing elements is omitted herein.

The example of FIG. 17 is different from that of FIG. 16 in that theformer example is provided with a fixed-rate detector 151, that thebuffer means are connected to the rear of the demultiplexer 96 and thataudio buffer means 152 and image buffer means 153 are separatelyprovided as the buffer means. Incidentally, operations of the composingelements of the example of FIG. 17 other than the reading operationcontroller 99, the fixed-rate detector 151 and the buffer means 152 and153 are similar to those of the same or corresponding elements of thefourth example.

In case of the fifth example, an audio is recorded on the recordingmedium by using a fixed transfer rate as illustrated in FIG. 18.Further, a reading operation is controlled in such a manner that atransfer rate of the audio information becomes constant, as will bedescribed later.

Information read by the information reading means 94 is immediatelyseparated by the demultiplexer 96 into audio information and imageinformation. Then, the audio information and the image information areinputted to the audio decoder 92 and the image decoder 97 through thebuffer means 152 and 153, respectively.

Furthermore, audio information outputted from the demultiplexer 96 isalso inputted to the fixed rate detector 151. In the fixed rate detector151, an amount of codes generated in a period of the predeterminedlength, which are generated from audio information outputted by thedemultiplexer 96 is measured. Thereafter, information representing theamount of the codes generated from the audio information is outputted tothe reading operation controller 99. The amount of the codes generatedby the audio information can be known by recording audio data composedof a set of audio information corresponding to each unit period of, forinstance, 100 ms.

Further, the information reading means 94 is controlled according to thereading operation control information sent from the reading operationcontroller 99 in such a way to read information from the recordingmedium or to stop a reading operation.

In the reading operation controller 99, it is judged from the audio codeamount information corresponding to the period of the predeterminedlength, which is inputted from the fixed rate detector 151, whether avalue indicated by the audio code amount information is less than ormore than a predetermined audio average transfer rate (namely, apredetermined average decoding rate). If less than, a reading operationis kept performed. In contrast, if more than, reading operation controlinformation, which indicates that a reading operation is inhibited andthat the information reading means is caused to stand by, is outputtedto the information reading means 94. Thus information can be read insynchronization with a decoding of audio information.

In this case, image information does not affect the control of theinformation reading means 49. As long as the image information isrecorded in such a manner that there is only a small difference betweena moment at which the image information is recorded and another momentat which the corresponding audio information is recorded, informationsufficient for a decoding can be obtained. Thus, there is not anoccurrence of an overflow in the buffer means 153.

Regarding the speed of the response of the information reading means 94to the control information, it is the same with the fourth example.However, it is unnecessary to record image information every period ofthe predetermined length as a packet of information. The controloperation can be easily performed.

Incidentally, audio information is employed as an example of the fixedrate information. However, other kinds of information recorded byutilizing a fixed transfer rate may be employed instead of audioinformation.

While the preferred embodiments of the present invention have beendescribed above, it is to be understood that the present invention isnot limited thereto and that other modifications will be apparent tothose skilled in the art without departing from the spirit of theinvention. The scope of the present invention, therefore, is to bedetermined solely by the appended claims.

What is claimed is:
 1. A variable transfer rate coding apparatus forcoding a plurality of moving picture signals in a total data stream,comprising: temporary coding means for quantizing each of the movingpicture signals in the total data stream according to a temporaryquantization step width which is determined according to each ofactivities of the moving picture signals to produce a plurality oftemporary quantized signals, changing the temporary quantized signals toa plurality of temporary variable length codes according to a variablelength coding and calculating a temporary transfer rate indicating anamount of temporary variable length codes in one prescribed time periodfor each of prescribed time periods, the plurality of temporary transferrates being variable with time; target transfer rate setting means forpreparing a plurality of transfer rate conversion characteristicsrespectively indicating the conversion of each temporary transfer ratecalculated by the temporary coding means to a target transfer rateindicating an amount of target codes in one prescribed time period,selecting a particular transfer rate conversion characteristic from theplurality of transfer rate conversion characteristics to provide aprescribed value for a total amount of target codes which are determinedby a plurality of target transfer rates obtained by converting thetemporary transfer rates corresponding to the moving picture signals inthe total data stream according to the particular transfer rateconversion characteristic, and calculating one target transfer rate fromeach of the temporary transfer rates according to the particulartransfer rate conversion characteristic, the plurality of targettransfer rates being variable with time, and each target transfer ratecorresponding to one prescribed time period; storingbuffer means fortemporarily storing codes, outputting the codes at one correspondingtarget transfer rate for each prescribed time period, the targettransfer rates for the prescribed time periods being variable with time,and outputting a buffer filling rate indicating a filling rateoccupancyinformation representing an occupancy degree of the codes in thestoringbuffer means; and real coding means for quantizing each of themoving picture signals in the total stream according to a realquantization step width which is determined according to each of theactivities of the moving picture signals and the buffer filling rateoccupancy information output from the storing buffer means to produce aplurality of real quantized signals so that a volume of variable lengthcodes obtained from each of the real quantized signals according to thevariable length coding is increased or decreased with the decrease orincrease of the buffer filling rate occupancy information and so that atotal sum of variable length codes obtained from the real quantizedsignals becomes the prescribed value, changing the real quantizedsignals to a plurality of real variable length codes having a totalvolume which is equal to the prescribed value according to the variablelength coding, and outputting the real variable length codes to thestoring buffer means one after another to output the real variablelength codes from the storing buffer means at one corresponding targettransfer rate for each prescribed time period, the target transfer ratesfor the prescribed time periods are variable with time.
 2. A variabletransfer rate coding apparatus according to claim 1 in which the targettransfer rate setting means comprises: a code amount controller forselecting the particular transfer rate conversion characteristics; and atarget transfer rate setting device for setting the target transfer ratefor each prescribed time period by converting each of the temporarytransfer rates into one target transfer rate according to the particulartransfer rate conversion characteristic selected by the code amountcontroller so that increase of the target transfer rates is less thanincrease of the temporary transfer rates and so that a maximum value ofeach of the target transfer rates is lower than a constant value.
 3. Avariable transfer rate coding apparatus according to claim 2 in whichthe code amount controller comprises: a plurality of transfer rateconverting devices for respectively converting one temporary transferrate into a converted transfer rate according to one of the transferrate conversion characteristic for each prescribed time period; aplurality of accumulation adders for respectively accumulating aplurality of converted transfer rates obtained from all the temporarytransfer rates in each of the transfer rate converting devices andrespectively generating a total amount of codes from the convertedtransfer rates; and a judgement device for selecting one total amount ofcodes having a maximum value from the total amounts generated in theaccumulation adders, the selected one total amount of codes being lowerthan a target total code amount, and selecting one transfer rateconversion characteristic relating to the selected one total amount ofcodes as the particular transfer rate conversion characteristic.
 4. Avariable transfer rate coding apparatus according to claim 3, in whichthe target total code amount in the judgement device denotes a recordingcapacity of a recording medium.
 5. A variable transfer rate codingapparatus according to claim 1 in which the temporary coding meanscomprises: a quantizer for quantizing each of the moving picture signalsin the total data stream according to the temporary quantization stepwidth for each prescribed time period; a variable length coder forcalculating the temporary variable length codes from the temporaryquantized signals obtained by the quantizer according to the variablelength coding; and a temporary code amount counter for calculating thetemporary transfer rate from the amount of the temporary variable lengthcodes for each prescribed time period.
 6. A variable transfer ratecoding apparatus according to claim 1 in which the real coding meanscomprises: a quantizer for quantizing each of the moving picture signalsin the total data stream according to the real quantization step widthfor each prescribed time period; a variable length coder for calculatingthe real variable length codes for each of the real quantized signalsobtained by the quantizer according to the variable length coding; and aquantization controller for adjusting the real quantization step widthaccording to the buffer filling rate occupancy information output fromthe storing buffer means to control the quantization performed by thequantizer.
 7. A variable transfer rate information reproducing apparatusfor reproducing pieces of moving picture information recorded on arecording medium, comprising: information reading means forintermittently reading the pieces of moving picture information from therecording medium at a constant information reading rate, the pieces ofmoving picture information being recorded coded at a variable transferrate changing every prescribed time period being recorded; buffer meansfor temporarily storing the pieces of moving picture information read bythe information reading means and outputting the pieces of movingpicture information at an information decoding rate; reading operationcontrolling means for detecting an occupancy information filling raterepresenting an occupancy degree of the buffer means and controlling areading operation performed by the information reading means accordingto the occupancy information filling rate to prevent an overflow of thepieces of moving picture information stored in the buffer means and aninformation empty condition of the buffer means; and decoding means fordecoding the pieces of moving picture information output from the buffermeans to obtain pieces of reproduced moving picture information.
 8. Avariable transfer rate information reproducing apparatus according toclaim 7 in which the information decoding rate is equal to or lower thanthe constant information reading rate, the reading operation performedby the information reading means is stopped under the control of thereading operation controlling means in cases where the occupancyinformation filling rate is higher than a prescribed upper limit, andthe reading operation stopped by the reading operation controlling meansis restarted under the control of the reading operation controllingmeans in cases where the occupancy information filling rate is lowerthan a prescribed lower limit.
 9. A variable transfer rate informationreproducing apparatus according to claim 7 in which the informationdecoding rate is changeable.
 10. A variable transfer rate informationreproducing apparatus according to claim 7 in which the readingoperation performed by the information reading means is continued underthe control of the reading operation controlling means to read thepieces of moving picture information stored in the buffer means induplicate as pieces of unnecessary information and discard theunnecessary information in cases where the information filling rate ishigher than a prescribed upper limit.
 11. A variable transfer rateinformation reproducing apparatus according to claim 7 in which thedecoding means comprises: a demultiplexer for demultiplexing each of thepieces of moving picture information to a piece of audio information anda piece of image information; an audio decoder for decoding the piecesof audio information obtained by the demultiplexer to obtain a piece ofreproduced audio information; and an image decoder for decoding thepieces of image information obtained by the demultiplexer to obtain apiece of reproduced image information.
 12. A variable transfer rateinformation reproducing apparatus for reproducing pieces of movingpicture information recorded on a recording medium, comprising:information reading means for intermittently reading at a constantinformation reading rate the pieces of moving picture information and apiece of reading operation control information from the recordingmedium, in which the pieces of moving picture information are recordedcoded at a variable transfer rate changing every prescribed time periodare recorded; buffer means for temporarily storing the pieces of movingpicture information read by the information reading means and outputtingthe pieces of moving picture information at an information decodingrate; control information separating means for separating the readingoperation control information from the pieces of moving pictureinformation read by the information reading means and controlling areading operation performed by the information reading means accordingto the reading operation control information to prevent an overflow ofthe pieces of moving picture information stored in the buffer means andan information empty condition of the buffer means; and decoding meansfor decoding the pieces of moving picture information output from thebuffer means to obtain pieces of reproduced moving picture information.13. A variable transfer rate information reproducing apparatus accordingto claim 12 in which the information decoding rate is equal to or lowerthan the constant information reading rate, and the reading operationperformed by the information reading means is stopped or restartedaccording to the reading operation control information to maintain anoccupancy information filling rate representing an occupancy degree ofthe buffer means within an allowable range.
 14. A variable transfer rateinformation reproducing apparatus according to claim 12 in which thedecoding means comprises: a demultiplexer for demultiplexing each of thepieces of moving picture information to a piece of audio information anda piece of image information; an audio decoder for decoding the piecesof audio information obtained by the demultiplexer to obtain a piece ofreproduced audio information; and an image decoder for decoding thepieces of image information obtained by the demultiplexer to obtain apiece of reproduced image information.
 15. A variable transfer rateinformation reproducing apparatus for reproducing pieces of movingpicture of information recorded on a recording medium, comprising:information reading means for intermittently reading the pieces ofmoving picture information and a piece of transfer rate information fromthe recording medium at a constant information reading rate for eachprescribed time period, in which the pieces of moving pictureinformation are recorded coded at a variable transfer rate changingevery prescribed time period, are recorded, the transfer rateinformation indicating the variable transfer rate; transfer rateinformation separating means for separating the transfer rateinformation from the pieces of moving picture information read by theinformation reading means; buffer means for temporarily storing thepieces of moving picture information read by the information readingmeans and outputting the pieces of moving picture information at aninformation decoding rate; reading operation controlling means forcontrolling a reading operation performed by the information readingmeans according to the transfer rate information obtained by thetransfer rate information separating means to prevent an overflow of thepieces of moving picture information stored in the buffer means and toprevent an information empty condition of the buffer means; and decodingmeans for decoding the pieces of moving picture information output fromthe buffer means to obtain pieces of reproduced moving pictureinformation.
 16. A variable transfer rate information reproducingapparatus according to claim 15 in which the information decoding rateis equal to or lower than the constant information reading rate, and thereading operation performed by the information reading means is stoppedor restarted under the control of the reading operation controllingmeans to maintain an occupancy information filling rate representing anoccupancy degree of the buffer means within an allowable range.
 17. Avariable transfer rate information reproducing apparatus according toclaim 15 in which the decoding means comprises: a demultiplexer fordemultiplexing each of the pieces of moving picture information to apiece of audio information and a piece of image information; an audiodecoder for decoding the pieces of audio information obtained by thedemultiplexer to obtain a piece of reproduced audio information; and animage decoder for decoding the pieces of image information obtained bythe demultiplexer to obtain a piece of reproduced image information. 18.A variable transfer rate information reproducing apparatus forreproducing pieces of moving picture information recorder in a packet ona recording medium for each prescribed time period comprising:information reading means for intermittently reading the pieces ofmoving picture information and code amount of the pieces of the movingpicture information in one packet from the recording medium at aconstant information reading rates for each prescribe time period, inwhich the pieces of moving picture information are recorded with achangeable amount of code indicating the pieces of the moving pictureinformation in one packet; packet code amount detecting means fordetecting the code amount of the pieces of moving pictures informationin one packet read by the information reading means for each prescribedtime period; buffer means for temporarily storing the pieces movingpicture information in one packet read by the information reading meansfor each prescribed time period and outputting the pieces of movingpicture information at an information decoding rate; reading operationcontrolling means for controlling a reading operation performed by theinformation reading means according to the code amount obtained by thepacket code amount detecting means to prevent an overflow of the piecesof moving picture information stored in the buffer means and aninformation empty condition of the buffer means; and decoding means fordecoding the pieces of moving picture information output from the buffermeans to obtain pieces of reproduced moving picture information.
 19. Avariable transfer rate information reproducing apparatus according toclaim 18 in which the information decoding rate is equal to or lowerthan the constant information reading rate, and the reading operationperformed by the information reading means is stopped or restarted underthe control of the reading operation controlling means to maintain anoccupancy information filling rate representing an occupancy degree ofthe buffer means within an allowable range.
 20. A variable transfer rateinformation reproducing apparatus according to claim 18 in which thedecoding means comprises: a demultiplexer for demultiplexing each of thepieces of moving picture information to a piece of audio information anda piece of image information; an audio decoder for decoding the piecesof audio information obtained by the demultiplexer to obtain a piece ofreproduced audio information; and an image decoder for decoding thepieces of image information obtained by the demultiplexer to obtain apiece of reproduced image information.
 21. A variable transfer rateinformation reproducing apparatus for reproducing pieces of movingpicture information recorded on a recording medium, comprising:information reading means for intermittently reading at a constantinformation reading rate the pieces of moving picture information fromthe recording medium, the pieces of moving picture information beingclassified into pieces of first information coded at a fixed transferrate and recorded on the recording medium at a fixed transfer rate andpieces of second information coded at a variable transfer rate changingevery prescribed time period and recorded on the recording medium at avariable transfer rate changing every prescribed time period, at aconstant information reading rate; demultiplexing means fordemultiplexing the pieces of moving picture information read by theinformation reading means to the pieces of first information and thepieces of second information; first buffer means for temporarily storingthe pieces of first information demultiplexed by the demultiplexingmeans and outputting the pieces of first information at an informationdecoding rate; second buffer means for temporarily storing the pieces ofsecond information demultiplexed by the demultiplexing means andoutputting the pieces of second information at the information decodingrate; fixed transfer rate detecting means for detecting the fixedtransfer rate from the pieces of first information; reading operationcontrolling means for controlling a reading operation performed by theinformation reading means according to the fixed transfer rate detectedby the fixed transfer rate detecting means to prevent an overflow of thepieces of first information stored in the first buffer means and toprevent an information empty condition of the first buffer means; firstdecoding means for decoding the pieces of first information output fromthe first buffer means to obtain pieces of reproduced first information;and second decoding means for decoding the pieces of second informationoutput from the second buffer means to obtain pieces of reproducedsecond information, pieces of reproduced moving picture informationbeing composed of the pieces of reproduced first information obtained bythe first decoding means and the pieces of second information.
 22. Avariable transfer rate information reproducing apparatus according toclaim 21 in which the information decoding rate is equal to or lowerthan the constant information reading rate, and the reading operationperformed by the information reading means is stopped or restarted underthe control of the reading operation controlling means to maintain anoccupancy information filling rate representing an occupancy degree ofthe first buffer means within an allowable range.
 23. A recording mediumon which codes are recorded, comprising: a recording region having aprescribed storing capacity value; and information of a plurality ofmoving picture signals in a total data stream being stored in therecording medium so that a sum of a plurality of real variable lengthcodes indicating the moving picture signals in the total data stream isequal to the prescribed storing capacity value, wherein each of themoving picture signals in the total data stream is quantized accordingto a temporary quantization step width which is determined according toeach of activities of the moving picture signals to produce a pluralityof temporary quantized signals which are changed to a plurality oftemporary variable length codes, a temporary transfer rate indicating anamount of temporary variable length codes in one prescribed time periodbeing calculated for each of prescribed time periods, a plurality oftarget transfer conversion characteristics respectively indicating theconversion of each of the temporary transfer rates to a target transferrate indicating an amount of target codes in one prescribed time periodare prepared, a particular target transfer conversion characteristicbeing selected from the plurality of target transfer conversioncharacteristics on condition that a total amount of target codes whichare determined by a plurality of target transfer rates obtained byconverting the temporary transfer rates corresponding to the movingpicture signals in the total data stream according to the particulartarget transfer conversion characteristic is the prescribed storingcapacity value of the recording region, one target transfer rate beingcalculated from each of the temporary transfer rates according to theparticular target transfer conversion characteristic on condition thatthe plurality of target transfer rates for the prescribed time periodsare variable with time, a buffer in which codes are temporarily stored,the codes are output at one corresponding target transfer rate for eachprescribed time period on condition that the target transfer rates forthe prescribed time periods are variable with time and that a bufferfilling rate indicating a filling rate of the codes in the buffer isoutput is prepared, each of the moving picture signals in the total datastream being quantized according to a real quantization step width whichis determined according to each of the activities of the moving picturesignals and the buffer filling rate output from the buffer to produce aplurality of real quantized signals on condition that a volume ofvariable length codes obtained from each of the real quantized signalsis increased or decreased with the decrease or increase of the bufferfilling rate and that a total sum of variable length codes obtained fromthe real quantized signals becomes the prescribed storing capacity valueof the recording region, the real quantized signals being changed to theplurality of real variable length codes of which a total volume is equalto the prescribed storing capacity value of the recording region, thereal variable length codes being temporarily stored in the buffer oneafter another, and the real variable length codes stored in the bufferare recorded in the recording region of the recording medium at onecorresponding target transfer rate for each prescribed time period oncondition that the plurality of target transfer rates for the prescribedtime periods are variable with time.
 24. A recording medium according toclaim 23, further comprising: reading operation control informationstored in the recording medium, wherein the information of the movingpicture signals in the total stream and the reading operation controlinformation are intermittently read from the recording region of therecording medium at a constant information reading rate, the readingoperation control information is separated from the information of themoving picture signals, the information of the moving picture signals istemporarily stored in a buffer unit and is output at an informationdecoding rate, a reading operation is controlled according to thereading operation control information to prevent an overflow of theinformation of the moving picture signals stored in the buffer unit andan information empty condition of the buffer unit, and the informationof the moving picture signals output from the buffer unit is decoded toobtain pieces of reproduced moving picture information.
 25. A variabletransfer rate coding apparatus for coding a plurality of moving picturesignals in a total data stream, comprising: temporary coding means forquantizing each of the moving picture signals in the total data streamaccording to a temporary quantization step width which is determinedaccording to each of activities of the moving picture signals to producea plurality of temporary quantized signals, changing the temporaryquantized signals to a plurality of temporary variable length codesaccording to a variable length coding and calculating a temporarytransfer rate indicating an amount of temporary variable length codes inone prescribed time period for each of prescribed time periods, theplurality of temporary transfer rates being variable with time; targettransfer rate setting means for setting a target transfer rate from eachof the temporary transfer rates calculated by the temporary coding meansso that a maximum value of each of the target transfer rates is lowerthan a prescribed constant value, and so as to provide a prescribedvalue for a total amount of target codes which are determined by aplurality of the target transfer rates corresponding to the movingpicture signals in the total data stream, the plurality of targettransfer rates being variable with time, and each target transfer ratecorresponding to one prescribed time period; buffer means fortemporarily storing codes, outputting the codes at one correspondingtarget transfer rate for each prescribed time period, the targettransfer rates for the prescribed time periods being variable with time,and outputting occupancy information representing an occupancy degree ofthe codes in the buffer means; and real coding means for quantizing eachof the moving picture signals in the total stream according to a realquantization step width which is determined according to each of theactivities of the moving picture signals and the occupancy informationoutput from the buffer means to produce a plurality of real quantizedsignals so that a volume of variable length codes obtained from each ofthe real quantized signals according to the variable length coding isincreased or decreased with the decrease or increase of the occupancyinformation and so that a total sum of variable length codes obtainedfrom the real quantized signals becomes the prescribed value, changingthe real quantized signals to a plurality of real variable length codeshaving a total volume which is equal to the prescribed value accordingto the variable length coding, and outputting the real variable lengthcodes to the buffer means one after another to output the real variablelength codes from the buffer means at the one corresponding targettransfer rate for each prescribed time period, the target transfer ratesfor the prescribed time periods being variable with time.
 26. A variabletransfer rate coding method for coding a plurality of moving picturesignals in a total data stream, comprising: a temporary coding step ofquantizing each of the moving picture signals in the total data streamaccording to a temporary quantization step width which is determinedaccording to each of activities of the moving picture signals to producea plurality of temporary quantized signals, changing the temporaryquantized signals to a plurality of temporary variable length codesaccording to a variable length coding and calculating a temporarytransfer rate indicating an amount of temporary variable length codes inone prescribed time period for each of prescribed time periods, theplurality of temporary transfer rates being variable with time; a targettransfer rate setting step of setting a target transfer rate from eachof the temporary transfer rates calculated by the temporary coding stepso that a maximum value of each of the target transfer rates is lowerthan a prescribed constant value, and so as to provide a prescribedvalue for a total amount of target codes which are determined by aplurality of the target transfer rates corresponding to the movingpicture signals in the total data stream, the plurality of targettransfer rates being variable with time, and each target transfer ratecorresponding to one prescribed time period; a buffering steps oftemporarily storing codes, outputting the codes at one correspondingtarget transfer rate for each prescribed time period, the targettransfer rates for the prescribed time periods being variable with time,and outputting occupancy information representing an occupancy degree ofthe codes in the buffering step; and a real coding step of quantizingeach of the moving picture signals in the total stream according to areal quantization step width which is determined according to each ofthe activities of the moving picture signals and the occupancyinformation output from the buffering step to produce a plurality ofreal quantized signals so that a volume of variable length codesobtained from each of the real quantized signals according to thevariable length coding is increased or decreased with the decrease orincrease of the occupancy information and so that a total sum ofvariable length codes obtained from the real quantized signals becomesthe prescribed value, changing the real quantized signals to a pluralityof real variable length codes having a total volume which is equal tothe prescribed value according to the variable length coding, andperforming the buffering step on the real variable length codes oneafter another to output the real variable length codes from thebuffering step at one corresponding target transfer rate for eachprescribed time period, the target transfer rates for the prescribedtime periods being variable with time.